Impact Factors on Airflow and Pollutant Dispersion in Urban Street Canyons and Comprehensive Simulations: a Review

Purpose of Review: The air quality management within urban street canyons can be improved by enhancing ventilation for dispersion of pollutants. The purpose of this review is to summarize effects of various impact factors on airflow and pollutant dispersion in urban street canyons. The relative intensity of different influence factors is reviewed, which should provide a useful comprehensive guide for modelling of these effects for urban developments. Recent Findings: All reviewed numerical simulations, wind tunnel and outdoor scaled model experiments show that the various building heights and incoming airflow conditions could produce a clear influence on airflow and pollutant dispersion in urban street canyon. Outdoor scaled experiments have provided complex turbulent data and illustrated the complexity of airflow within urban street canyons, which would require comprehensive simulations to investigate the microclimate within these urban street canyons. Summary: Impacts of thermal and/or wall heating conditions have been fully studied, while the impact of inflow variation, building height difference, model scale and the coupling effect of different factors are current hot topics for research. Building height difference and time-varying inflow conditions are factors of most significant influence, while tree planting, vehicle-induced turbulence, thermal and/or wall heat conditions have a relatively weak influence.